Resonant pressure switch

ABSTRACT

A pressure sensor integrated onto an electronic circuit substrate. The pressure sensor measures the effect of the ambient air pressure on a characteristic of the pressure sensor that can be translated into a variable pressure measurement. Another embodiment of the pressure sensor is a pressure switch having a set point that can be configured at, or after, the time of installation of the associated circuit substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. applicationSer. No. 10/096,566, filed Mar. 13, 2002.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not Applicable.

BACKGROUND OF THE INVENTION

[0003] 1. Field of Invention

[0004] The present invention relates to the field of pressure sensors.More specifically, the present invention relates to a pressure sensorintegrated onto a circuit substrate.

[0005] 2. Description of the Related Art

[0006] Pressure sensors are known to those skilled in art. Typically,these devices fall into two categories. In the first category areset-point pressure sensors, more properly referred to as pressureswitches, that actuate when a specified pressure is reached. The secondcategory contains the more sophisticated pressure sensors, that arecapable of measuring the ambient pressure and reacting accordingly.Generally, pressure switches are less complex and more cost efficientthan pressure sensors.

[0007] In low tire pressure warning systems, a typical mass-marketapplication, the critical function of the warning system is to identifywhen the tire pressure falls below a specified value. Accordingly, usinga pressure sensor with the ability to measure the tire pressure addsextra expense to the system.

[0008]FIG. 1 illustrates an exploded view of a conventional pressureswitch. The conventional pressure switch includes a base member 11having tabs 12 for securing the conventional pressure switch on acircuit board. Connected to the base member 11 is a metal enclosure 13.A hollow contact pin 14 passes through an opening in the base of themetal enclosure 13 and allows the pressure of and/or the gas within thepressure switch to be changed. A non-conductive end piece 15 serving asa diaphragm support is attached to the end of the contact pin 14terminating within the metal enclosure 13. A thin metal diaphragm 17covers the open end of the metal enclosure 13. A metal spring 16 biasesthe end piece 15 and the contact pin 14 against the diaphragm 17. Themetal spring 16, in combination with the hollow contact pin 14, isselected to set the pressure at which the switch responds. A cover 18having a small, central through opening 19 provides protection for thediaphragm 17.

BRIEF SUMMARY OF THE INVENTION

[0009] An apparatus integrated onto an electronic circuit substrate,which may be a circuit board or a semiconductor-based product formeasuring the ambient pressure, a pressure sensor, or sensing when theambient pressure reaches a specified value, a pressure switch, is shownand described. The pressure switch is considered to be a subset of thegeneral pressure sensor. The pressure sensor is low profile andreliable. When implemented as a pressure switch, it has a set point thatcan be configured at, or after, the time of installation of theassociated circuit substrate. Further, the pressure sensor can containother electrical components to conserve valuable circuit substrate realestate and allow the construction of self-contained electronic pressuresensors.

[0010] In one embodiment, the pressure sensor is an absolute pressureswitch including a fluid-tight sealed enclosure having one surface thatacts as a diaphragm. At least one other surface of the pressure sensoris formed from a circuit substrate. The internal volume of the pressureswitch is typically small and is maintained at the atmospheric pressurewhere and when the pressure sensor is sealed. Variations in the ambientair pressure relative to the internal pressure force the diaphragm tomove thereby making or breaking contact with an electrical conductorthat completes the switch. Finally, the internal volume can be filledwith either atmospheric gases or with an inert gas selected to preventoxidation or to change the set point characteristics.

[0011] In both the pressure sensor and the pressure switch, thediaphragm is secured to the open end of the enclosure in a fluid-tightmanner, completing the sealed enclosure. The diaphragm is constructedfrom an electrically conductive, flexible material. The diaphragmincludes a series of concentric grooves to provide extra flexibilitysuch that the diaphragm can move without deformation. Both the top andbottom surfaces of the diaphragm are provided with a set of concentricgrooves. Within each set, the concentric grooves are equally spaced;however, the top set and the bottom set are offset from one another. Thepresent inventors have found that this arrangement provides increasedflexibility and responsiveness in the diaphragm. The diaphragm isdesigned to exhibit flexibility and allow movement in response to apressure differential between the ambient pressure and the internalpressure of the pressure sensor.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0012] The above-mentioned features of the invention will become moreclearly understood from the following detailed description of theinvention read together with the drawings in which:

[0013]FIG. 1 illustrates a conventional pressure switch according to theprior art;

[0014]FIG. 2 illustrates one embodiment of a circuit substrateintegrated pressure switch;

[0015]FIG. 3 is a top plan view of a diaphragm for use with a pressuresensor;

[0016]FIG. 4 is a sectional view of the diaphragm of FIG. 3;

[0017]FIG. 5 illustrates, in partial section, one embodiment of thepressure switch of the present invention;

[0018]FIG. 6 illustrates, in partial section, an alternate embodiment ofthe pressure switch of the present invention;

[0019]FIG. 7 illustrates a pressure switch of the present inventionincluding internal circuitry;

[0020]FIG. 8 is a perspective view of a pressure sensor fabricated in adual inline package integrated circuit;

[0021]FIG. 9 is an exploded perspective view of one embodiment-of apressure sensor incorporating a microwave oscillator and a microwaveresonator as the sensing element;

[0022]FIG. 10 is a sectional view of one embodiment of a pressure sensoradapted for the sensing of pressure changes using the capacitiveproperty of a dielectric filler material;

[0023]FIG. 11 is an exploded perspective view of a one embodiment of apressure sensor incorporating an electrically conductive rubber pill asa dielectric filler material for the measurement of pressure based onresistivity changes induced by the deflection of the diaphragm;

[0024]FIG. 12 is an exploded perspective view of one embodiment of apressure sensor fabricated in an integrated circuit packageincorporating a generic sensing element;

[0025]FIG. 13 is an exploded perspective view of one embodiment of apressure sensor fabricated in an integrated circuit packageincorporating a microwave resonance circuit for the measurement ofpressure;

[0026]FIG. 14 is an exploded perspective view of one embodiment of apressure sensor incorporating an optical sensor pair for the measurementof pressure using the effects on a beam by the deflection of thediaphragm; and

[0027]FIG. 15 is is an exploded perspective view of a one embodiment ofa pressure sensor incorporating an inductor for the measurement ofpressure based on inductance changes induced by the deflection of thediaphragm.

DETAILED DESCRIPTION OF THE INVENTION

[0028] An apparatus integrated onto an electronic circuit substrate forsensing the ambient pressure, or pressure sensor, is described and showngenerally at 10 in the figures. The pressure sensor 10 measures theambient pressure based on perturbations of a known characteristic causedby flexing of a diaphragm exposed to the ambient pressure. The pressuresensor 10 is adaptable to trip when the ambient pressure reaches aspecified value, in effect operating as a pressure switch. The pressuresensor 10 is low profile and reliable. When configured as a pressureswitch, the pressure sensor has a set point that can be configured at,or after, the time of installation of the associated circuit substrate.Further, the pressure sensor 10 can contain other electrical componentsto conserve valuable circuit substrate real estate and allow theconstruction of self-contained electronic pressure sensors. As usedherein, pressure switch is a subset of the more general class ofpressure sensors with the basic structure of the pressure switches andthe pressure sensors being substantially similar. The differencesbetween the pressure sensor and the pressure switches being the type ofdetection components used therein.

[0029]FIG. 2 illustrates a circuit substrate integrated pressure switch10 of the present invention. The pressure switch 10 is an absolutepressure switch including a fluid-tight sealed enclosure having onesurface that acts as a diaphragm 202. At least one other surface of thepressure switch is formed from a circuit substrate 204. In theillustrated embodiment, the enclosure is built using a spacer ring 206.The internal volume of the pressure switch 10 is typically small and ismaintained at the atmospheric pressure where and when the pressureswitch 10 is sealed. Variations in the ambient air pressure flex thediaphragm 202 thereby making or breaking contact with an electricallyconductive member 208 that completes the pressure switch 10. In theillustrated embodiment, the conductive member 208 has a substantiallyspherical shape and the circuit substrate is shown as a printed circuitboard (PCB).

[0030] The term circuit substrate is intended to refer to any circuitsubstrate upon which a circuit can be formed, including semiconductormaterials and printed circuit boards. More specifically, the use of theterm circuit substrate is intended to cover integrated circuitimplementations using common miniaturization techniques, for example,large-scale integration and very large-scale integration. FIG. 8illustrates an integrated circuit implementation of the pressure sensor800. In the illustrated embodiment, the integrated circuit is a commondual inline package 802. The diaphragm 804 is exposed in a mannersimilar to that employed when exposing the window of an electricallyerasable programmable read-only memory or a photosensitive element in aintegrated circuit based photosensor. The use of other available packagetypes for integrated circuit implementations of the pressure sensor willbe appreciated by those skilled in the art. Those skilled in the artwill also recognize that applicability of the fabrication of thepressure sensor or pressure switch in a microelectromechanical system.

[0031]FIG. 3 illustrates a top plan view of the diaphragm 202. Thediaphragm 202 is constructed from an electrically conductive, flexiblematerial, such as a spring temper metal, i.e., phosphorous bronze. Inthe illustrated embodiment, the diaphragm 202 has a circular shape.Those skilled in the art will recognize that the diaphragm can beconstructed from other materials exhibiting the desired flexibility andcould have other shapes without departing from the spirit and scope ofthe present invention. The diaphragm 202 includes a series of concentricgrooves 302 to provide extra flexibility such that the diaphragm canmove without deformation. One method of creating the grooves 302 is bychemically etching the diaphragm. Those skilled in the art willrecognize that other methods of creating the grooves 302, includingstamping and other machining techniques, can be used without departingfrom the spirit and scope of the present invention.

[0032]FIG. 4 illustrates a cross-section of the diaphragm 202 shown inFIG. 3. In the illustrated embodiment, both the top 402 and bottomsurface 404 of the diaphragm are provided with a set of concentricgrooves 406, 408. Within each set 406, 408, the concentric grooves areequally spaced; however, the top set 406 and the bottom set 408 areoffset from one another. The present inventors have found that thisarrangement provides increased flexibility and responsiveness in thediaphragm 202. In the illustrated embodiment, the top set 406 and thebottom set 408 are offset by one-half of the groove spacing. Thoseskilled in the art will recognize that other groove patterns, groovespacings, and groove offsets can be used without departing from thespirit and scope of the present invention. The diaphragm 202 is designedto exhibit flexibility and allow movement in response to a pressuredifferential between the ambient pressure and the internal air pressureof the pressure sensor 10.

[0033]FIG. 5 illustrates one embodiment in which the pressure sensor 10includes at least one ring 502 stacked on the surface of the circuitsubstrate 504 to create an open-ended enclosure having the desiredvolume. In the illustrated embodiment, the enclosure is a cylinder withthe circuit substrate forming the base of the enclosure. A trace 506matching the shape of the enclosure is printed on the circuit substrateto define the enclosure position. The material from which the rings 502are formed is not critical; however, the rings 502 are typically solidmetal or metal laminated. A solder paste coating on the rings 502provides the sealing mechanism when heated and serves to form agas-impermeable barrier when semi-porous materials are used. The solderpaste-coated rings 502 are permanently seated on the circuit substrate504 by placing the circuit substrate in a reflow oven. The presentinventors have found that the rings 502 substantially align as thesolder paste flows during heating and that no special alignment effortis necessary to achieve a sealed enclosure. Those skilled in the artwill recognize that, while rings 502 and a generally cylindricalenclosure are described herein, other shapes may be used withoutdeparting from the scope and spirit of the present invention. Thediaphragm serves as the top of the enclosure and flexes in response tothe ambient pressure. The flex of the diaphragm provides a mechanism toperform switching based upon ambient pressure and to vary acharacteristic of the pressure sensor which can be translated into avariable pressure measurement.

[0034] The circuit substrate defines a through opening 508 providingaccess to the interior of the enclosure. The through opening 508 isdimensioned to receive a conductive member that serves to define the setpoint of the pressure switch. It is desirable, but not necessary, forthe conductive member to be constructed from the same metal as thediaphragm. This reduces the effect of galvanic corrosion. In addition,those skilled in the art will recognize that the electric connection canbe maximized by increasing the contact geometry between the conductivemember and the diaphragm. One method of achieving the increased contactarea when using an elongated conductive member is to shear the contactend of the member such that it presents a flat surface normal to thediaphragm.

[0035] In another embodiment, illustrated in FIG. 6, the enclosure ofthe pressure switch 600 is formed using the thickness of the circuitsubstrate 602. In this embodiment, the circuit substrate 602 defines alarge diameter through opening 604. A trace 606 is etched around theedges of the through opening 604 which cooperates with the solder pasteto provide the sealing function. A base plate 608 is secured to one sideof the circuit substrate 602 and a diaphragm 610 is secured to theopposite side of the circuit substrate 602 to seal the through opening604 in a fluid-tight manner. The base plate 608 defines a contactopening adapted to receive a conductive member 612. The end of theconductive member 612 is positioned at a distance relative to or incontact with the diaphragm 610 while the pressure switch 600 is underpressure to define the appropriate set point. The conductive member 612is secured in a fluid-tight manner, e.g., soldered into place.

[0036] The embodiment of FIG. 6 further defines a separate pressurevalve opening 614. The pressure valve opening 614 is used to establishthe internal pressure of the pressure switch and to facilitate theexchange of gases within the pressure switch. For many applications, thepressure switch 600 can operate using standard atmospheric gases;however, those skilled in the art will recognize that the internalvolume of the pressure switch 600 can be filled with an inert gas toprevent oxidation. The pressure valve opening 614 facilitates changes tothe internal pressure or fill gas that are independent of thepositioning of the conductive member 612. Once the desired internalpressure or internal gas is established, the pressure valve opening 614is sealed in a fluid-tight manner. Those skilled in the art willrecognize that the pressure valve opening 614 can be closed in apermanent manner, preventing later modifications, or temporary manner,facilitating later modifications, without departing from the spirit andscope of the present invention. Further, those skilled in the art willrecognize that the features provided by the pressure valve opening 614can be achieved using the contact opening, thereby obviating the needfor multiple fluid-tight seals to be maintained.

[0037] In the embodiment illustrated in FIG. 6, the conductive member isan elongated member such as a wire or pin. To assign a set point, thepressure switch is placed under pressure. Typically this is achieved byapplying a calibrated pressure on the diaphragm to induce movement. Theconductive member is then inserted through the through opening in thebottom of the volume until it is brought in contact with the distendedbottom surface of the diaphragm and soldered into place to create afluid-tight seal. When pressure is released, the diaphragm returns to anunflexed position thereby placing the pressure switch into its normalstate. Depending upon the application, the pressure switch can beconfigured to react when the ambient pressure either goes above or belowa selected set point. For example, in the application of a low tirepressure warning system, the pressure switch is set at the desiredwarning pressure. While the tire pressure exceeds the set point of thepressure switch, i.e., a positive pressure differential, the pressureswitch remains closed. As the tire pressure decreases and approaches thewarning pressure, the diaphragm of the pressure switch deflectsoutwardly in response to the lowering of the ambient pressure. In thiscondition, the pressure switch opens signaling that the tire pressure islow. Conversely, in an application that requires monitoring of anincrease in the ambient air pressure above a particular set point, thepressure switch is higher and the switch remains normally open. When theambient air pressure equals or exceeds the set point pressure, thediaphragm deflects inwardly and the pressure switch closes.

[0038] In an alternate embodiment, such as illustrated in FIG. 2, theconductive member has a substantially spherical shape. To produce ahighly accurate and precise pressure switch, the conductive member is aprecision ball bearing ground to specification. However, othersubstantially spherically shaped conductive members can be used withdeparting from the scope and spirit of the present invention. The setpoint of the pressure switch is adjusted without the need to apply anexternal pressure to the pressure switch. Specifically, the set point isadjusted by selecting a bearing of a desired diameter which correspondsto a set point for a pressure switch of particular dimensions. Thebearing is sealed in the through opening of the enclosure. Alternately,the diameter of the bearing can remain constant and the diameter of theenclosure through opening can be varied to change the height at whichthe bearing sits relative to the diaphragm. The use of a bearing for theconductive member simplifies final assembly of the pressure switch.Further, if the diameter of the through opening is used as the set pointvariable, the required assembly inventory is minimized.

[0039]FIG. 7 illustrates an exploded view of an alternate embodiment ofthe pressure switch 700 including internal circuitry 702 not necessarilyrelated to the operation of the pressure switch 700. The components andtraces that are disposed within the volume of the enclosure do notinterfere with the operation of the pressure switch. Accordingly, bylocating components and traces on the circuit substrate real estateinternal to the enclosure of the pressure switch, miniaturization andprotection of the circuit is realized.

[0040] In another embodiment, two pressure switches are disposedback-to-back to provide a range over which the pressure switch operates.Typically, such an arrangement would involve a multi-layer circuitsubstrate with a central conductor. Two opposing enclosures would beformed each having its own contact member, and diaphragm. By configuringthe dual pressure switch with two set points, the pressure switcheffectively operates to monitor a pressure with a certain range. Such anarrangement can also be used to monitor two related pressures, such as awarning pressure and a critical pressure.

[0041] Thus far, the pressure switches described herein are implementedutilizing manual/mechanical method of calibration, i.e., establishing aset-point by the positioning of a conductive pin or the selection of asphere of a specified diameter. Alternatively, the pressure switch canbe calibrated electronically with no mechanical intervention other thanan initial calibration pressure applied to the system. For example, whenthe initial calibration pressure is applied to the pressure switch, theelectronics are set in a mode that stores the frequency reading. Thevalues read during the calibration are stored in a memory element. Thoseskilled in the art will appreciate the use of non-volatile memoryelements, such as an electrically erasable programmable read only memory(EEPROM) or any of the common memory card formats in use and the use ofregisters or other holding units in processing devices, which may becoupled with other types of memory elements. This initial frequencyreading serves as the initial calibration point. The controllercalculates the correct conversion of the initial frequency to a pressurevalue based upon known control constants. Those skilled in the art willrecognize that multiple calibration points, such as calibrations at theupper and lower end of the detection range, can be established in thesame manner. The initiation of the calibration mode is accomplishedusing techniques known to those skilled in the and depending upon theenvironment where the pressure switch is located. Such techniquesinclude manual activation of an accessible switch, remote control,programmatic control. An example of one common technique is the use of amagnetic reed switch to trigger a calibration mode on a pressure switchlocated inside a tire. Those skilled in the art will recognize that theelectrical calibration techniques described herein can be used with anyof the pressure switch or pressure sensor embodiments described herein.

[0042] The basic structure described herein can also be adapted forpressure sensing applications. The various embodiments of the pressuresensor described herein offers enhanced resistance to problemsassociated with temperature. FIG. 9 illustrates a pressure sensor 900adapted to respond to a resonator element 902 and an associatedoscillator circuit 904 disposed within the volume 906 of the enclosure.Pressure on the outside of the diaphragm 906 causes it to flex inwardlyinto the enclosure thereby reducing the volume 904 of the enclosure andthe distance between the diaphragm 908 and the resonator element 902.The resonant frequency of the pressure switch 900 varies with thedistance between the diaphragm 908 and the resonator element 902 and theoscillator circuit 902 is responsive to the resonant frequency of theresonant cavity. The resonant frequency represents an instant pressurevalue. Thus, the pressure sensor 900 is capable of variable pressuremeasurement meaning that it is capable of identifying an instantpressure value rather than being limited to indicating when a certainset-point threshold has been crossed.

[0043] Those skilled in the art will recognize that various sizes,geometries, and types of resonator elements can be employed withoutdeparting from the scope and spirit of the present invention. Forexemplary purposes, it will be understood that both stripline andmicrostrip resonators can be used. A stripline resonator is typicallysymmetrical with a ground plane on each side of the resonator. Theground planes associated with the stripline resonator illustratedinclude the diaphragm and a ground plane disposed on the opposing faceof the circuit substrate. The minor differences in the relative distancebetween the stripline resonator and each ground plane can be accountedfor without disrupting the function of the stripline resonator. Amicrostrip resonator is typically half of the dimensions of thestripline resonator and relies on a single ground plane, which isdisposed on one side of the microstrip resonator, such as on theopposing face of the circuit substrate. Various geometries, for example,ring, hairpin, and line resonators are suitable for use. Further,acceptable resonator elements are sized according to the desiredfrequency response characteristics. The resonator element can be a traceon the circuit substrate or can be a separate component connected to thecircuit substrate or pressure sensor.

[0044] The oscillator circuit 904 is selected to work within a frequencyrange of interest, including but not limited to radio frequency,microwave frequency, and low frequency. In the illustrated embodiment,the oscillator circuit 904 is disposed within the volume 904 of theenclosure to implement a self-contained pressure sensor. However, theoscillator circuit 904 may alternatively be positioned outside of theenclosure without departing from the scope and spirit of the presentinvention.

[0045] The resonant cavity has a known field distribution at a givenambient pressure. A small perturbation in the resonant cavity causes theresonant frequency to shift. Generally, a small perturbation in a cavitywall has an varying effect on each of the electric energy and themagnetic energy of the cavity. The shift in resonant frequency occurs inan attempt to equalize the electric and magnetic energies. Oneexpression defining the relationship of the cavity volume to the volumeperturbation is: $\begin{matrix}{{\frac{\Delta \quad f_{r}}{f_{r}} = {\frac{\int_{\Delta \quad V}^{\quad}{\left( {{\mu \quad H^{2}} - {ɛ\quad E^{2}}} \right)\quad {V}}}{\int_{\quad V}^{\quad}{\left( {{\mu \quad H^{2}} + {ɛ\quad E^{2}}} \right)\quad {V}}} = \frac{\int_{\Delta \quad V}^{\quad}{\left( {{\mu \quad H^{2}} - {ɛ\quad E^{2}}} \right)\quad {V}}}{4\quad U}}},} & (1)\end{matrix}$

[0046] where ΔV is the volume perturbation and Δf_(r) is the change inthe resonant frequency. The electrical energy and magnetic energy willvary depending upon the shape and volume of the resonant cavity and theoperation mode. Those skilled in the art will recognize other accepteddefinitions associated with resonance changes. With the inclusion of theresonator element, the pressure sensor 900 can be adapted to beresponsive to the resonant frequency of the cavity, to the resonantfrequency of the resonator element, or to a composite resonant frequencyinfluenced by both the cavity and the resonator element.

[0047] In an alternate embodiment, the resonator element is omittedleaving the resonant frequency tied solely to the volume of theenclosure, which serves as a resonant cavity. The frequency of theoscillator circuit varies with the volume of the enclosure, which isdependent on the flex of the diaphragm. As the volume of the enclosureis reduced, the resonant frequency of the enclosure changes.

[0048] In another embodiment, the resonant frequency pressure sensorincludes an adjustment member that is inserted into the cavity throughan opening in the enclosure. By varying the amount of insertion, thevolume of the enclosure is modified. This permits modification of theresonant frequency of the cavity independent of the effects of flex onthe diaphragm. One embodiment of the adjustment member utilizes a screwthat can be adjustably inserted or retracted as desired withoutrequiring the adjustment member to be permanently secured. In anotherembodiment, the adjustment member is a pin that is inserted to set adesired resonant frequency and then substantially permanently securedthrough a method such a soldering. Those skilled in the art willrecognize other structures that can be effectively used for theadjustment member that can be temporarily or permanently secured in theenclosure and other methods that can be used to the achieve the desiredtemporary or permanent fixation without departing from the scope andspirit of the present invention. In one embodiment, the adjustmentmember is a pin of temperature stable resistive matter, or resistivepin. The resistive pin acts as a direct pressure to resistance sensorthat can be electronically calibrated or combined with mechanicalcalibration.

[0049] The variable pressure measurement of the pressure sensor ismeasured in units of relative pressure (psir) to a reference pressurecharacterized by the resonant frequency of the cavity at a known state.The pressure sensor is calibrated by signaling the controller to set thefrequency at a known state. In one embodiment, the selected frequency isthe frequency associated with the mid-range of a known applied pressureduring factor calibration. A simple frequency measuring circuit orfrequency counter is implemented to convert the frequency measurement toa pressure value, which allows for variable pressure measurement.

[0050] In a further embodiment, the diaphragm is configured to engage apiezoelectric element, for example, a piezoelectric crystal, within thepressure sensor. When the diaphragm presses, stresses, or otherwisealters the piezoelectric element, the low frequency structure resonanceis varied. This allows for responses at frequencies below the recognizedfloor of the radio frequency spectrum. The piezoelectric pressure sensoris well-suited for low power operation and can be implemented in anintegrated circuit.

[0051] Other embodiments of the pressure sensor incorporate a fillermaterial within the cavity. The filler material is a fluid exhibiting aproperty that can be varied by a change in volume of the cavity or bythe deflection of the diaphragm. The fluid typically has dielectric orelectrolytic characteristics. This property is generally measurablethrough techniques known to those skilled in the art. Examples of fillermaterial properties that can be influenced to sense a change in pressureinclude changes in capacitance, resistance, inductance, and voltage.

[0052]FIG. 10 illustrates a cross section of a pressure sensor 1000adapted for the sensing of pressure changes using the capacitiveproperty of a dielectric filler material. The dielectric filler materialis typically a conductive material from which a capacitance can bemeasured and exhibiting a variable capacitance related to changes involume or pressure. Examples of suitable filler materials include aconductive rubber material or a dielectric fluid, including air.

[0053] A circuit substrate 1006 provides support for the pressure sensor1000. An electrically conductive ring 1012 and a diaphragm 1010,together with the circuit substrate 1006 form an enclosure which definesa volume 1002. A filler material 1002 substantially fills the volume ofthe pressure sensor 1000. A plate 1004 disposed on the circuit substrate1006, together with diaphragm 1010, form the plates of a capacitor. Thedielectric properties of the filler material 1002 influence the chargebetween the plates 1004, 1010 of the capacitor. When the diaphragm 1010is flexed, it interacts with the filler material 1002 and, with thechange in the separation distance between the plates 1004, 1010, thecapacitance changes. This variation in capacitance provides a measurableproperty for the sensing of a change in pressure. A plurality of vias1008, 1014 allow for an electrical connection to each of the plates1004, 1010 of the capacitor. Other methods electrical connection will beappreciated by those skilled in the art.

[0054] A simple capacitance measurement circuit, known to those skilledin the art, is used to measure the capacitance of the filler material.The measured capacitance value represents the pressure value. Thiscapacitance can also affect an oscillator circuit at resonance where thechange in capacitance corresponds to a change in the pressure to whichthe sensor is exposed. Those skilled in the art will recognize othercircuits which can be used to measure the capacitance without departingfrom the scope and spirit of the present invention. It will be furtherappreciated by those skilled in the art that numerical storage methodslend themselves to firmware calibration allowing for the development ofa highly integrated circuit. For example, associated EEPROM cells placedin parallel with the pressure sensor can be set on or off to offer aphysical trim of the capacitance providing a method of fine tuning thecapacitance measurement.

[0055] In a similar manner, the resistance of a filler material can bemeasured to determine the pressure on the sensor. Examples of suitablefiller materials include an electrically conductive rubber material or adielectric fluid exhibiting a variable resistance under pressure orvolume fluctuations. The filler material substantially fills the volumeof the enclosure. When the diaphragm is flexed, it interacts with thefiller material to alter the resistance of the filler material. FIG. 11illustrates one embodiment of a pressure sensor 1100 including anelectrically conductive rubber pill 1102 disposed within the enclosure.The electrically conductive rubber pill 1102 presents connects thediaphragm 1104 and a conductor 1106. A simple resistance measurementcircuit known to those skilled in the art is used to measure theresistance of the filler material. The measured resistance valuerepresents the pressure value. This resistance can also affect anoscillator circuit at resonance where the change in resistancecorresponds to a change in the pressure to which the sensor is exposed.

[0056]FIG. 15 illustrates an alternate embodiment of a pressure sensor1500 wherein the inductance is measured to determine the pressure on thesensor. An oscillator (not shown) generates an inductive field withinthe pressure sensor. When flexed, the diaphragm 1502 perturbs theinductive field of present in the cavity. The illustrated embodimentincludes an inductive coil assembly 1504 disposed on the circuitsubstrate 1506. The inductive coil assembly 1504 is a bobbin having acoil of wire wrapped around it. In an alternate embodiment, theunderside of the diaphragm 1502 includes an attachment, for example adome, that is adapted to extend closer to or into the inductive coilassembly 1504 to enhance the perturbation of the inductive field. In yetanother alternative embodiment, the inductive coil assembly is replacedby a monolithic flat inductor disposed on the circuit substrate. Asimple inductance measurement circuit, for example a frequency counter,known to those skilled in the art is used to measure the changesfrequency of the inductive field. The measured inductance valuerepresents the pressure value.

[0057] The signal produced by the various embodiments of the pressuresensor is processed according to the demands of the application wherethe pressure sensor is installed. In applications requiring littleprecision and a simple visual indication of relative pressure, theoutput of the pressure sensor can be used to directly drive anindicator, such as a light-emitting diode bar. In applications requiringmore precision or additional processing, the output of the pressuresensor can be interfaced with a processing device. A typicalimplementation involves feeding the output of the pressure sensor into asignal conditioning circuit. The signal conditioning circuit conditionsthe pressure sensor output into form that is useful for furtherprocessing. Such processing generally includes amplification of thesignal and can include filtering. In an analog circuit application, theconditioned signal is fed into a comparator circuit and the output ofthe comparator circuit serves as a decision point in determining furtheraction. In a digital circuit application, the conditioned signal is thenfed into an analog-to-digital converter and the digital output isgenerally acted upon a digital processing device, such as amicrocontroller, a digital signal processor, or a microprocessor, toperform additional functions or provide detailed outputs. The pressureoutput can be logged and stored for long term monitoring of a process orfor later, post-processing analysis.

[0058]FIG. 12 is an exploded illustration of one embodiment of thepressure sensor 1200 fabricated in the form of a self-contained chip, orintegrated circuit. A diaphragm 1202 and a ring 1204, if necessary, arestacked on a circuit substrate 1206 to build the pressure sensor 1200.In the illustrated embodiment, a sensing element 1208 is shown on thecircuit substrate 1206 within the volume of the pressure sensor 1200.The circuit substrate 1206 includes a number of pins 1210 which can beelectrically connected to the components of pressure sensor 1200 orother unrelated internal circuitry as desired. The pressure sensor 1200,via pins 1210, can be placed in physical and electrical communicationwith a separate circuit board using standard mating techniques,including but not limited to socketing and soldering. FIG. 13illustrates an exploded view of one embodiment of a pressure sensor 1300utilizing a microwave resonator circuit 1302 as the sensing element.

[0059] Alternate embodiments of the pressure sensor utilizesphotosensitive or “optical” technologies for sensing pressure. Thephotosensitive embodiments described herein are not intended to belimited to light in any one spectrum and various wavelengths of light,including but not limited to the visible, infrared, and ultravioletspectrums, can be used without departing from the scope and spirit ofthe present invention. FIG. 14 illustrates an exploded view of oneembodiment of an optical deflection pressure sensor 1400. The opticaldeflection pressure sensor 1400 detects changes in the deflection angleof a beam of light. The optical beam deflection pressure sensor includesat least one emitter element 1402 and at least one detector element1404. The diaphragm is adapted so as to be reflective to the beam oflight. The emitter element 1402 is disposed so that the emitted beamstrikes the diaphragm 1406 and is reflected to the detector element1404. The position at which the beam strikes the detector element 1404is used to determine the deflection. Movement of the diaphragm 1406 inresponse to changes in the ambient pressure results in changes in theangle of deflection. The change in the angle of deflection provides anoutput that corresponds to the change in pressure. Those skilled in theart will recognize that the emitter element 1402 and the detectorelement 1404 can be fabricated using single elements, an array ofdiscrete elements, or from a single element configured in multiplesections. While the diaphragm 1406 described herein is inherentlyreflective, those skilled in the art will appreciate that the diaphragmmay be polished to enhance the reflectiveness or a reflective film ormember can be secured to the underside of the diaphragm withoutdeparting from the scope and spirit of the present invention.

[0060] A similar embodiment detects changes in the intensity of thereflected beam. The emitter and detector are arranged such that underthe default pressure the full intensity of the beam strikes thedetector. Changes in the ambient pressure cause deflection of thediaphragm that, in turn, change the deflection of the beam. As thedeflection of the beam changes, the energy of the beam incident on thedetector varies. The energy value, which is the output of the pressuresensor, corresponds to the change in pressure. In another alternateembodiment, an extension, which is typically angled, on the diaphragmserves to interrupt members of an array of direct beams to detectposition.

[0061] Finally, in the area of optical technologies, another embodimentuses optical resonance to measure the change in pressure. The opticalresonance embodiment includes an arrangement of mirrors within thecavity. A resonant wavelength of a light source from an emitter isestablished within the cavity. The resonant wavelength seen by thedetector varies with deflection of the diaphragm. One technique foroptical resonance pressure measurement uses the Fabry-Perot cavitysensor. The Fabry-Perot method is extendable to the pressure sensorstructure described herein.

[0062] In an alternate embodiment, a pressure sensor adapted formeasuring the ambient pressure in any of the embodiments described abovealso includes the features of the pressure switch described herein. Theset-point pressure switch adds a separate pressure detection circuitthat can operate as a fail-safe in the event of a malfunction withregard to the ambient pressure measure. The combination pressure sensorand pressure switch provides an integrated under a single diaphragm. Theredundant sensing allows for an instantaneous switch response withoutthe need to rely on another circuit or device to produce a responsebased upon a logical analysis of the pressure sensor output. Thecombination pressure sensor and pressure switch implementation isextremely robust, self-testing, and redundant without requiring anyadditional circuit substrate real estate. Further, the combinationpressure sensor and pressure switch adds additional functionalityallowing for a broader range of applications where the combinationpressure sensor and pressure switch can be used effectively.

[0063] Those skilled in the art will recognize that the logic describedherein can be implemented in either hardware and/or software using anyof the typical technologies used to implement control functionsincluding discrete logic, application specific integrated circuits,custom integrated circuits, microcontrollers, microprocessors, and anycombination thereof. Where circuit diagrams and block or flow diagramsof circuits have been illustrated, those skilled in the art willrecognize that the diagrams are intended to illustrate the generalconcept and functionality of the device. Common circuit components thatwill be familiar to one skilled in the art of circuit design, such aspower connections, feedback, trimming, and voltage regulationcomponents, are not necessarily illustrated. A pressure switch andpressure sensor that is integrated into a circuit substrate has beenshown and described. The pressure switch provides a low cost, easilymanufactured, durable, simple-to-assemble device for detecting when anambient pressure reaches a selected set point. The pressure sensordisclosed herein allow the measurement of the current ambient pressureon the pressure sensor. Various embodiments having a number of uniqueimplementations, features, and functions have been described herein.Those skilled in the art will recognize that, unless mutually exclusive,the implementations, features, and functions can be combined withoutdeparting from the scope and spirit of the present invention. Oneexample of function that can be used in combination with each of theembodiments described is the variable calibration system.

[0064] A number of various features and embodiments of both pressureswitches and pressure sensors have been described herein. While allcombinations of features and embodiments have not been expresslydescribed, it will be understood that the various features andembodiments can be combined to achieve the desired pressure sensor orpressure switch without departing from the scope and spirit of thepresent invention. For example, the adjustment of the cavity volumeusing an adjustment member, the resistive pin, and the electrical andmanual calibration techniques are applicable to all embodimentsdescribed herein.

[0065] While the present invention has been illustrated by descriptionof several embodiments and while the illustrative embodiments have beendescribed in detail, it is not the intention of the applicant torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. The invention in its broader aspects istherefore not limited to the specific details, representative apparatusand methods, and illustrative examples shown and described. Accordingly,departures may be made from such details without departing from thespirit or scope of applicant's general inventive concept.

Having thus described the aforementioned invention, we claim:
 1. Apressure sensor responsive to an ambient pressure, said pressure sensorcomprising: a cavity defining a volume, said cavity including: anenclosure having an upper opening and a plurality of surfaces includinga bottom surface and at least one side surface, one of said plurality ofsurfaces being formed from a circuit substrate; and a diaphragm coveringsaid upper opening, said diaphragm forming a fluid-tight seal with saidenclosure, said diaphragm responsive to the ambient pressure; and asensing element in communication with said cavity, said sensing elementhaving a property that varies with either of said volume and adeflection of said diaphragm, said property being readable by ameasurement circuit.
 2. The pressure sensor of claim 1 wherein saidcircuit substrate is a printed circuit board.
 3. The pressure sensor ofclaim 1 wherein said circuit substrate is a semiconductor material. 4.The pressure sensor of claim 1 wherein said frequency varies with saidvolume of said resonant cavity.
 5. The pressure sensor of claim 1wherein said cavity is a microwave resonant cavity.
 6. The pressuresensor of claim 1 wherein said sensing element is an oscillator.
 7. Thepressure sensor of claim 6 wherein said oscillator operates in afrequency range selected from the group consisting of microwavefrequencies, radio frequencies, and low frequencies.
 8. The pressuresensor of claim 7 wherein said oscillator operates in said microwavefrequency range, said pressure sensor further comprising a microwaveresonator element disposed within said cavity, said microwave resonatorelement and said diaphragm being selected by a distance.
 9. The pressuresensor of claim 8 wherein said frequency varies with said distancebetween said diaphragm and said microwave resonator element. Thepressure sensor of claim 8 wherein said microwave resonant element is astripline resonator.
 10. The pressure sensor of claim 8 wherein saidmicrowave resonant element is a microstrip resonator.
 11. The pressuresensor of claim 1 wherein said diaphragm is constructed of a flexible,conductive material.
 12. The pressure sensor of claim 11 wherein saidflexible, conductive material is a spring-temper metal.
 13. The pressuresensor of claim 1 wherein said diaphragm has a top surface and a bottomsurface, said diaphragm defining a plurality of concentric grooves onsaid top surface.
 14. The pressure sensor of claim 13 wherein saiddiaphragm further defines a plurality of concentric grooves on saidbottom surface.
 15. The pressure sensor of claim 14 wherein saidplurality of concentric grooves on said bottom surface is offset fromsaid plurality of concentric grooves on said top surface.
 16. Thepressure sensor of claim 1 wherein said cavity further defines a throughopening adapted to receive an adjustment member.
 17. The pressure sensorof claim 16 wherein said adjustment member is variably extended andretracted into said cavity to adjust said volume of said resonantcavity.
 18. The pressure sensor of claim 16 wherein said adjustmentmember is inserted into said cavity to adjust said volume of saidcavity, said volume adjustment member being substantially permanentlyfixed in a selected position.
 19. The pressure sensor of claim 16wherein said adjustment member is a screw capable of being variablyextended and retracted into said cavity to adjust said volume of saidcavity.
 20. The pressure sensor of claim 16 wherein said adjustmentmember is an elongated member that is inserted into said cavity toadjust said volume of said cavity, said volume adjustment member beingsubstantially permanently fixed in a selected position.
 21. The pressuresensor of claim 16 wherein said adjustment member is an elongated memberof temperature stable resistive matter.
 22. The pressure sensor of claim1 wherein a known calibration pressure is applied to said pressuresensor, said pressure sensor further comprising a memory element forstoring an initial value associated with said calibration pressure. 23.The pressure sensor of claim 22 wherein said memory element is anon-volatile memory device.
 24. The pressure sensor of claim 22 whereinsaid memory element is an electrically erasable programmable read onlymemory.
 25. The pressure sensor of claim 1 further comprising an opticalemitter and an optical detector, said optical detector adapted to detectan optical beam emitted by said optical emitter and deflected by saiddiaphragm.
 26. The pressure sensor of claim 1 further comprising anelectrically conductive member within said cavity and electricallyinsulated from said cavity, said electrically conductive memberpositioned such that said electrically conductive member makeselectrical contact with said diaphragm when a pressure applied to saidpressure sensor exceeds a selected pressure.
 27. The pressure sensor ofclaim 1 wherein said sensing element is a filler material substantiallyfilling said volume of said cavity, said filler material having acharacteristic that varies in response to deflection of said diaphragm.28. The pressure sensor of claim 27 wherein said filler materialcharacteristic is capacitance.
 29. The pressure sensor of claim 27wherein said filler material characteristic is resistance.
 30. Thepressure sensor of claim 27 wherein said filler material characteristicis inductance.
 31. The pressure sensor of claim 1 wherein said sensingelement property is frequency.
 32. A pressure sensor responsive to anambient air pressure, said pressure sensor comprising: means forenclosing a volume; means for varying said volume in response to theambient air pressure; means for sensing a change in said volume; andmeans for producing an output corresponding to said change in saidvolume.
 33. The pressure sensor of claim 32 wherein said means forenclosing a volume is an enclosure having a plurality of surfaces, atleast one of said surfaces being formed from a circuit substrate.
 34. Apressure sensor responsive to an ambient air pressure, said pressuresensor comprising: means for enclosing a volume including a means forsupporting a circuit; means for varying said volume in response to theambient air pressure; means for sensing a change in said volume; andmeans for producing an output corresponding to said change in saidvolume.
 35. A pressure switch responsive to an ambient air pressure,said pressure switch comprising: an enclosure defining an internalvolume and an upper opening, said enclosure having a plurality ofsurfaces including a bottom surface and at least one side surface, oneof said plurality of surfaces being formed from a circuit substrate; adiaphragm covering said upper opening, said diaphragm forming afluid-tight seal with said enclosure; and a conductive member adapted tocooperate with said diaphragm to signal when the ambient air pressurereaches a set point, said set point defined by a position of saidconductive member relative to said diaphragm at a selected ambient airpressure.
 36. The pressure switch of claim 35 wherein said diaphragm isconstructed of a flexible, conductive material.
 37. The pressure switchof claim 36 wherein said flexible, conductive material is aspring-temper metal.
 38. The pressure switch of claim 35 wherein saiddiaphragm has a top surface and a bottom surface, said diaphragmdefining a plurality of concentric grooves on said top surface.
 39. Thepressure switch of claim 38 wherein said diaphragm further defines aplurality of concentric grooves on said bottom surface.
 40. The pressureswitch of claim 39 wherein said plurality of concentric grooves on saidbottom surface is offset from said plurality of concentric grooves onsaid top surface.
 41. The pressure switch of claim 35 wherein saidenclosure further defines a through opening adapted to receive saidconductive member, said through opening having a diameter.
 42. Thepressure switch of claim 41 wherein said conductive member is asubstantially spherical member having a diameter, said set point beingdefined by said through opening diameter and said substantiallyspherical member diameter.
 43. The pressure switch of claim 35 whereinconductive member is an elongated member, said set point being definedby positioning said elongated member relative to said diaphragm while areference pressure is applied to said diaphragm.
 44. A pressure sensorresponsive to an ambient pressure, said pressure sensor comprising: acavity defining a volume, said cavity having a resonant frequency, saidcavity including: an enclosure having an upper opening and a pluralityof surfaces including a bottom surface and at least one side surface,one of said plurality of surfaces being formed from a circuit substrate;and a diaphragm covering said upper opening, said diaphragm forming afluid-tight seal with said enclosure, said diaphragm responsive to theambient pressure; and an oscillator circuit responsive to said resonantfrequency, said resonant frequency varying with deflection of saiddiaphragm, said oscillator circuit producing an output corresponding tosaid resonant frequency.
 45. A pressure sensor responsive to an ambientpressure, said pressure sensor comprising: a cavity defining a volume,said cavity including: an enclosure having an upper opening and aplurality of surfaces including a bottom surface and at least one sidesurface, one of said plurality of surfaces being formed from a circuitsubstrate; and a diaphragm covering said upper opening, said diaphragmforming a fluid-tight seal with said enclosure, said diaphragmresponsive to the ambient pressure; a resonator element disposed withinsaid cavity, said resonator element having a resonant frequency; and anoscillator circuit responsive to said resonant frequency, said resonantfrequency varies as a distance between said diaphragm and said resonatorelement changes, said oscillator circuit producing an outputcorresponding to said resonant frequency.
 46. A pressure sensorresponsive to an ambient pressure, said pressure sensor comprising: acavity defining a volume, said cavity including: an enclosure having anupper opening and a plurality of surfaces including a bottom surface andat least one side surface, one of said plurality of surfaces beingformed from a circuit substrate; and a diaphragm covering said upperopening, said diaphragm forming a fluid-tight seal with said enclosure,said diaphragm responsive to the ambient pressure; a dielectric fillersubstantially filling said volume; a plate disposed within said cavity,said plate cooperating with said diaphragm to form a variable capacitor,said capacitance varying as a distance between said diaphragm and saidplate changes.
 47. A pressure sensor responsive to an ambient pressure,said pressure sensor comprising: a cavity defining a volume, said cavityincluding: an enclosure having an upper opening and a plurality ofsurfaces including a bottom surface and at least one side surface, oneof said plurality of surfaces being formed from a circuit substrate; anda diaphragm covering said upper opening, said diaphragm forming afluid-tight seal with said enclosure, said diaphragm responsive to theambient pressure; an inductor disposed within said cavity, saidinductance varying as said diaphragm perturbs an inductive field.
 48. Apressure sensor responsive to an ambient pressure, said pressure sensorcomprising: a cavity defining a volume, said cavity including: anenclosure having an upper opening and a plurality of surfaces includinga bottom surface and at least one side surface, one of said plurality ofsurfaces being formed from a circuit substrate; and a diaphragm coveringsaid upper opening, said diaphragm forming a fluid-tight seal with saidenclosure, said diaphragm responsive to the ambient pressure; and adielectric filler material substantially filling said cavity, saiddielectric filler material having a property that varies with adeflection of said diaphragm, said property being readable by ameasurement circuit.
 49. A pressure sensor responsive to an ambientpressure, said pressure sensor comprising: a cavity defining a volume,said cavity including: an enclosure having an upper opening and aplurality of surfaces including a bottom surface and at least one sidesurface, one of said plurality of surfaces being formed from a circuitsubstrate; and a diaphragm covering said upper opening, said diaphragmforming a fluid-tight seal with said enclosure, said diaphragmresponsive to the ambient pressure; and an optical emitter disposedwithin said cavity, said optical emitter producing a beam directed atsaid diaphragm; an optical detector disposed within said cavity, saidoptical detector cooperating with said optical emitter to sensing saidbeam deflected by said diaphragm, said beam indicating an amount ofdeflection of said diaphragm by either an angle of deflection of saidbeam or a measurement of power incident on said optical detector, saidoptical detector producing an output associated with said amount ofdeflection which corresponds to the ambient pressure on said pressuresensor.